To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
In general, a wireless communication system assumes a Gaussian distribution with respect to an interference signal to conduct decoding with low complexity. That is, to make characteristics of the interference signal as close to the Gaussian distribution as possible, the QAM modulation scheme is mostly used. However, since it is known that a channel capacity of a non-Gaussian channel is greater than a Gaussian channel, when the decoding is conducted properly, a higher decoding performance can be obtained in the non-Gaussian channel than the Gaussian channel. Thus, it was required to develop a modulation scheme allowing the characteristics of the interference signal to exhibit the non-Gaussian distribution, and as a result, a suggested modulation scheme is the FQAM. The FQAM is a hybrid modulation scheme combining the QAM and the FSK, and can include all of advantages of high spectrum efficiency of the QAM and a non-Gaussian interference signal of the FSK.
When the FQAM is used in an interference cell, statistical characteristic of the interference signal becomes non-Gaussian and accordingly a non-Gaussian decoding method needs to be used to enhance the performance through the FQAM. The non-Gaussian decoding method is a decoding method using a statistical characteristic value (hereafter, referred to as an ‘alpha value) of the interference signal. To systematically operate the non-Gaussian decoding method, it is required to calculate the alpha value in the process of Channel Quality Indicator (CQI) calculation and to calculate the alpha value in the process of data decoding as well. To minimize a performance loss, there should be no difference between the alpha value of the CQI calculation and the alpha value of the data decoding. However, in the system operation, a difference value inevitably occurred between the alpha value of the CQI calculation and the alpha value of the data decoding.